Post-processing circuit for weak echo signal of CMUT sensor

Abstract

The utility model discloses a weak echo signal post-processing circuit for a CMUT sensor. A forward voltage input module is sequentially connected with a power supply port of a forward input end of a power supply of an echo signal I-V conversion amplification module and a power supply port of a forward input end of a power supply of an eight-order Butterworth band-pass filtering module; the reverse voltage input module is sequentially connected with a power supply port of a power supply reverse input end of the echo signal I-V conversion amplification module and a power supply port of a power supply reverse input end of the eight-order Butterworth band-pass filtering module; and the output port of the echo signal I-V conversion amplification module is connected to the input port of the eight-order Butterworth band-pass filtering module. The utility model meets the requirement that the input bias voltage and current are as small as possible, reduces the power consumption, and reduces the load of the signal source; and the gain bandwidth product meets the range requirement of ultrasonic detection.

Description

Technical Field

[0001] This utility model belongs to the field of MEMS electronic measurement technology, and mainly relates to the field of CMUT (Capacitive Micromachined Ultrasonic Transducer) echo signal post-processing, specifically involving a high-frequency weak echo signal processing circuit for ultrasonic transducer echoes. Background Technology

[0002] With the development of micro-electro-mechanical systems (MEMS) technology, capacitive micromachined ultrasonic transducers (CMUTs), as an advanced ultrasonic transducer, have broad application prospects in fields such as medical diagnosis and industrial inspection due to their advantages such as high sensitivity, wide bandwidth, ease of arraying and integration.

[0003] The working principle of a CMUT (CMoutlet transducer) is based on detecting ultrasonic signals through capacitance changes. When ultrasound acts on the CMUT transducer, it causes the transducer membrane to vibrate, thereby changing the capacitance between the membrane and the substrate, and generating a weak current signal, i.e., an echo signal. In practical applications, due to the small size and limited capacitance of individual CMUT microarray elements, the echo signal strength is extremely low. Even in ultrasonic scenarios using CMUT array transducers, the echo signal is typically in the nA range. Such a weak signal is highly susceptible to external electromagnetic interference, thermal noise, and internal system noise during transmission, resulting in a significant deterioration in signal quality, which in turn affects subsequent processing and overall system performance.

[0004] In existing ultrasound imaging systems, the weak echo signals received by the CMUT transducer are typically amplified using traditional amplifier circuits, i.e., two-stage amplifier circuits. The first stage amplification uses a transimpedance amplifier to convert the input micro-current signal into a voltage signal. However, the voltage signal after the first stage amplification often has a low amplitude due to insufficient amplification, thus requiring a second stage amplification. For noise processing, digital filtering is commonly used, primarily Kalman filtering. Its basic principle is to recursively combine predicted and observed data to optimally estimate the system state, thereby achieving filtering. It features high real-time performance and computational efficiency, and can provide relatively accurate estimates in linear systems. However, Kalman filtering also has some limitations: first, it is based on the assumption of linear systems and performs poorly in nonlinear systems; second, the estimation accuracy decreases when the observed noise and system noise are high; and third, it requires accurate system models and noise statistics, which are often difficult to meet in practical applications. Although this method is often used for processing weak high-frequency echo signals, existing solutions often suffer from problems such as insufficient amplification factor of the transimpedance amplifier, low center frequency of the bandpass filter, narrow passband bandwidth, and insufficient stopband attenuation, resulting in a low signal-to-noise ratio for high-frequency nA level current signals.

[0005] In summary, it is necessary to study high-performance, high-quality post-processing technology for high-frequency weak signals to convert current signals into voltage signals, filter out high-frequency and low-frequency noise, improve spurious resistance, eliminate self-excited oscillations, and improve the tailing phenomenon. This is of great significance for obtaining effective echo signals in noise. Utility Model Content

[0006] To address the disordered self-oscillations and noise in the echo signals received in the CMUT transceiver circuit, this invention proposes an amplification and analog filtering circuit for high-frequency weak signals. The aim is to solve the problem of self-oscillations and noise mixed in the high-frequency weak echo signals received in the echo circuit, attenuate the amplitude of self-oscillations, filter out high-frequency and low-frequency noise, and retain and amplify the nA level echo signals.

[0007] The technical solution adopted by this utility model to solve the key technical problem is:

[0008] A post-processing circuit for weak echo signals from a CMUT sensor includes a positive voltage input module, a reverse voltage input module, an echo signal IV conversion and amplification module, and an eighth-order Butterworth bandpass filter module.

[0009] The forward voltage input module is connected in sequence to the forward power input port of the echo signal IV-to-conversion amplifier module and the forward power input port of the eighth-order Butterworth bandpass filter module; the reverse voltage input module is connected in sequence to the reverse power input port of the echo signal IV-to-conversion amplifier module and the reverse power input port of the eighth-order Butterworth bandpass filter module; the output port of the echo signal IV-to-conversion amplifier module is connected to the input port of the eighth-order Butterworth bandpass filter module.

[0010] The eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multi-feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multi-feedback circuit. The output port of the echo signal IV conversion amplifier circuit is connected to the input port of the first-stage second-order active bandpass multi-feedback circuit; the output port of the first-stage second-order active bandpass multi-feedback circuit is connected to the input port of the first-stage LC parallel resonant filter amplifier circuit; the output port of the first-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage LC parallel resonant filter amplifier circuit; and the output port of the second-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage second-order active bandpass multi-feedback circuit.

[0011] In the positive voltage input module, the VCC input port is connected to the positive voltage input port 6 of the IV conversion amplifier chip U1, the positive voltage input port 7 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the positive voltage input port 7 of the first-stage LC parallel resonant filter amplifier circuit U3, the positive voltage input port 7 of the second-stage LC parallel resonant filter amplifier circuit U4, and the positive voltage input port 7 of the second-stage second-order active bandpass multi-feedback amplifier chip U5; capacitors C4 and C5 are connected in parallel, with the first end connected to the positive voltage input port 6 of the IV conversion amplifier chip U1 and the second end grounded; capacitor C10 and capacitor C5 are connected in parallel. Capacitor C11 is connected in parallel, with its first end connected to the positive voltage input port 7 of the amplifier chip U2 in the first-stage second-order active bandpass multiple feedback circuit, and its second end grounded; capacitors C15 and C16 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U3 in the first-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C20 and C21 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U4 in the second-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C26 and C27 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U5 in the second-stage second-order active bandpass multiple feedback circuit, and their second end grounded.

[0012] In the reverse voltage input module, the VDD input port is connected to the reverse voltage input port 2 of the IV conversion amplifier chip U1, the reverse voltage input port 4 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the reverse voltage input port 4 of the first-stage LC parallel resonant filter amplifier circuit U3, the reverse voltage input port 4 of the second-stage LC parallel resonant filter amplifier circuit U4, and the reverse voltage input port 4 of the second-stage second-order active bandpass multi-feedback amplifier chip U5, respectively; capacitors C6 and C7 are connected in parallel, with the first end connected to the reverse voltage input port 2 of the IV conversion amplifier chip U1 and the second end grounded; capacitor C12 and capacitor C7 are connected in parallel. Capacitor C13 is connected in parallel, with its first end connected to the inverted voltage input port 4 of the amplifier chip U2 in the first-stage second-order active bandpass multiple feedback circuit, and its second end grounded; capacitors C17 and C18 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U3 in the first-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C22 and C23 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U4 in the second-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C28 and C29 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U5 in the second-stage second-order active bandpass multiple feedback circuit, and their second end grounded.

[0013] In the echo signal IV conversion and amplification module, resistor R1 and capacitor C2 are connected in parallel, with the first end connected to the positive input terminal of amplifier U1 and the second end grounded; resistor R2 and capacitor C3 are connected in parallel, with the first end connected to the inverting input terminal of amplifier U1 and the second end connected to the output terminal Vin of amplifier U1; the first end of capacitor C1 is connected to the echo signal input terminal Iin, and the second end is connected to the inverting input terminal of amplifier U1.

[0014] In the first-stage second-order active bandpass multiple feedback circuit, the first end of resistor R3 is connected to the output terminal Vin of the echo signal IV conversion amplification module, and the second end is connected to the first end of resistor R4, the first end of capacitor C8, and the first end of capacitor C9; the second end of resistor R4 is grounded; the second end of capacitor C8 is connected to the output terminal Vout1 of amplifier U2; the second end of capacitor C9 is connected to the inverting input terminal of amplifier U2; the first end of resistor R5 is connected to the output terminal Vout1 of amplifier U2, and the second end is connected to the inverting input terminal of amplifier U2; the non-inverting input terminal of amplifier U2 is grounded.

[0015] In the first-stage LC parallel resonant filter amplifier circuit, the first end of resistor R6 is connected to the output terminal Vout1 of the first-stage second-order active bandpass multiple feedback circuit, and the second end is connected to the positive input terminal of amplifier U3; inductor L1 and capacitor C14 are connected in parallel, with the first end connected to the positive input terminal of amplifier U3 and the second end grounded; the first end of resistor R7 is connected to the inverting input terminal of amplifier U3, and the second end is connected to the output terminal Vout2 of amplifier U3; the first end of resistor R8 is connected to the inverting input terminal of amplifier U3, and the second end is grounded.

[0016] In the second-stage LC parallel resonant filter amplifier circuit, the first end of resistor R9 is connected to the output terminal Vout2 of the first-stage LC parallel resonant filter amplifier circuit, and the second end is connected to the positive input terminal of amplifier U4; inductor L2 and capacitor C19 are connected in parallel, with the first end connected to the positive input terminal of amplifier U4 and the second end grounded; the first end of resistor R10 is connected to the inverting input terminal of amplifier U4, and the second end is connected to the output terminal Vout3 of amplifier U4; the first end of resistor R11 is connected to the inverting input terminal of amplifier U4, and the second end is grounded.

[0017] In the second-stage second-order active bandpass multiple feedback circuit structure, the first terminal of resistor R12 is connected to the output terminal Vout3 of the second-stage LC parallel resonant filter amplifier circuit, and the second terminal is connected to the first terminal of resistor R13, the first terminal of capacitor C24, and the first terminal of capacitor C25; the second terminal of resistor R13 is grounded; the second terminal of capacitor C24 is connected to the output terminal Vout4 of amplifier U5; the second terminal of capacitor C25 is connected to the inverting input terminal of amplifier U5; the first terminal of resistor R14 is connected to the output terminal Vout4 of amplifier U5, and the second terminal is connected to the inverting input terminal of amplifier U5; the non-inverting input terminal of amplifier U5 is grounded.

[0018] Compared with the prior art, this utility model patent has the following advantages:

[0019] (1) Compared with the traditional IV conversion circuit, the echo signal IV conversion circuit meets the requirements of minimizing input bias voltage and current, thus reducing power consumption; it meets the requirement of maximizing input resistance, thus reducing the load on the signal source; and the gain-bandwidth product meets the range requirements of ultrasonic detection.

[0020] (2) Compared with the traditional IV conversion circuit, this design solves the problem of insufficient amplification factor of the preamplifier output voltage signal. Under the premise of filtering out high-frequency and low-frequency noise, it can also attenuate the amplitude of self-excited oscillation, improve the amplification factor of the circuit, and meet the design requirements.

[0021] (3) Compared with the traditional IV-only conversion circuit, an eighth-order Butterworth bandpass filter circuit is introduced to quickly attenuate the amplitude of signals in non-desired frequency bands, effectively suppress noise signals outside the range, and improve the signal-to-noise ratio of the final output signal.

[0022] (4) Compared with the traditional multi-stage amplifier circuit + bandpass filter, this design adopts a single-stage amplifier + eighth-order Butterworth bandpass filter, which not only reduces the number of stages that need to be amplified, but also increases the order of the bandpass filter and improves the filtering effect. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the bandwidth-adjustable IV converter amplifier circuit of this utility model;

[0024] Figure 2 This is a schematic diagram of the first-stage second-order active bandpass multiple feedback circuit of this utility model;

[0025] Figure 3 This is a schematic diagram of the first-stage LC parallel resonant filter amplifier circuit of this utility model;

[0026] Figure 4 This is a schematic diagram of the second-stage LC parallel resonant filter amplifier circuit of this utility model;

[0027] Figure 5 This is a schematic diagram of the second-stage second-order active bandpass multiple feedback circuit of this utility model;

[0028] Figure 6 This is a schematic diagram of the overall circuit of this utility model;

[0029] Figure 7 This is a simulation diagram of the gain Bode's ratio of the IV conversion amplifier circuit of this utility model;

[0030] Figure 8 This is a simulation diagram of the gain and Baud rate of the IV conversion amplifier circuit + eighth-order Butterworth bandpass filter circuit of this utility model. Detailed Implementation

[0031] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0032] A post-processing circuit for high-frequency weak echo signals of CMUT sensors includes: a forward voltage input module, a reverse voltage input module, an echo signal IV conversion and amplification module, and an eighth-order Butterworth bandpass filter module.

[0033] The forward voltage input module is connected in sequence to the forward power input port of the echo signal IV-to-conversion amplifier module and the forward power input port of the eighth-order Butterworth bandpass filter module; the reverse voltage input module is connected in sequence to the reverse power input port of the echo signal IV-to-conversion amplifier module and the reverse power input port of the eighth-order Butterworth bandpass filter module; the output port of the echo signal IV-to-conversion amplifier module is connected to the input port of the eighth-order Butterworth bandpass filter module.

[0034] The eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multi-feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multi-feedback circuit. The output port of the echo signal IV-to-Volume conversion amplifier circuit is connected to the input port of the first-stage second-order active bandpass multi-feedback circuit; the output port of the first-stage second-order active bandpass multi-feedback circuit is connected to the input port of the first-stage LC parallel resonant filter amplifier circuit; the output port of the first-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage LC parallel resonant filter amplifier circuit; and the output port of the second-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage second-order active bandpass multi-feedback circuit. The overall circuit structure is as follows: Figure 6 As shown.

[0035] The positive voltage input module includes: a VCC input port, capacitors C4, C5, C10, C11, C15, C16, C20, C21, C26, and C27; the VCC input port is connected to the positive voltage input port 6 of the IV conversion amplifier chip U1, the positive voltage input port 7 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the positive voltage input port 7 of the first-stage LC parallel resonant filter amplifier circuit U3, the positive voltage input port 7 of the second-stage LC parallel resonant filter amplifier circuit U4, and the positive voltage input port 7 of the second-stage second-order active bandpass multi-feedback amplifier chip U5; capacitors C4 and C5 are connected in parallel, with their first terminals connected to the IV conversion amplifier. The positive voltage input port 6 of the large chip U1 is connected to ground; capacitors C10 and C11 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U2, which is a first-stage second-order active bandpass multiple feedback circuit, and their second end connected to ground; capacitors C15 and C16 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U3, which is a first-stage LC parallel resonant filter amplifier circuit, and their second end connected to ground; capacitors C20 and C21 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U4, which is a second-stage LC parallel resonant filter amplifier circuit, and their second end connected to ground; capacitors C26 and C27 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U5, which is a second-stage second-order active bandpass multiple feedback circuit, and their second end connected to ground.

[0036] The reverse voltage input module includes: a VDD input port, capacitors C6, C7, C12, C13, C17, C18, C22, C23, C28, and C29; the VDD input port is connected to the reverse voltage input port 2 of the IV conversion amplifier chip U1, the reverse voltage input port 4 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the reverse voltage input port 4 of the first-stage LC parallel resonant filter amplifier circuit U3, the reverse voltage input port 4 of the second-stage LC parallel resonant filter amplifier circuit U4, and the reverse voltage input port 4 of the second-stage second-order active bandpass multi-feedback amplifier chip U5; capacitors C6 and C7 are connected in parallel, with their first terminals connected to the IV conversion amplifier... The inverted voltage input port 2 of the large chip U1 is connected to ground; capacitors C12 and C13 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U2 in the first-stage second-order active bandpass multiple feedback circuit, and their second end connected to ground; capacitors C17 and C18 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U3 in the first-stage LC parallel resonant filter amplifier circuit, and their second end connected to ground; capacitors C22 and C23 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U4 in the second-stage LC parallel resonant filter amplifier circuit, and their second end connected to ground; capacitors C28 and C29 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U5 in the second-stage second-order active bandpass multiple feedback circuit, and their second end connected to ground.

[0037] The echo signal I-V conversion and amplification module includes: amplifier U1, resistors R1 and R2, capacitors C1, C2, and C3, and an echo signal input port; resistors R1 and C2 are connected in parallel, with their first end connected to the positive input terminal of amplifier U1 and their second end grounded; resistors R2 and C3 are connected in parallel, with their first end connected to the inverting terminal of amplifier U1 and their second end connected to the output terminal Vin of amplifier U1; the first end of capacitor C1 is connected to the echo signal input terminal Iin, and its second end is connected to the inverting input terminal of amplifier U1.

[0038] The eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multi-feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multi-feedback circuit.

[0039] The first-stage second-order active bandpass multiple feedback circuit adopts an active filter structure using the infinite gain multiple feedback method, including: amplifier U2, resistors R3, R4, and R5, capacitors C8 and C9; the first terminal of resistor R3 is connected to the output terminal Vin of the echo signal IV conversion amplification module, and the second terminal is connected to the first terminal of resistor R4, the first terminal of capacitor C8, and the first terminal of capacitor C9; the first terminal of resistor R4 is connected to the second terminal of R3, and the second terminal is grounded; the first terminal of capacitor C8 is connected to the second terminal of resistor R3, and the second terminal is connected to the output terminal Vout1 of amplifier U2; the first terminal of capacitor C9 is connected to the second terminal of resistor R3, and the second terminal is connected to the negative input terminal of amplifier U2; the first terminal of resistor R5 is connected to the output terminal Vout1 of amplifier U2, and the second terminal is connected to the negative input terminal of amplifier U2; the positive input terminal of amplifier U2 is grounded.

[0040] The first-stage LC parallel resonant filter amplifier circuit includes: amplifier U3, resistors R6, R7, and R8, inductor L1, and capacitor C14; the first end of resistor R6 is connected to the output terminal Vout1 of the first-stage second-order active bandpass multiple feedback circuit, and the second end is connected to the positive input terminal of amplifier U3; inductor L1 and capacitor C14 are connected in parallel, with the first end connected to the positive input terminal of amplifier U3 and the second end grounded; the first end of resistor R7 is connected to the negative input terminal of amplifier U3, and the second end is connected to the output terminal Vout2 of amplifier U3; the first end of resistor R8 is connected to the negative input terminal of amplifier U3, and the second end is grounded.

[0041] The second-stage LC parallel resonant filter amplifier circuit includes: amplifier U4, resistors R9, R10, and R11, inductor L2, and capacitor C19; the first end of resistor R9 is connected to the output terminal Vout2 of the first-stage LC parallel resonant filter amplifier circuit, and the second end is connected to the positive input terminal of amplifier U4; inductor L2 and capacitor C19 are connected in parallel, with the first end connected to the positive input terminal of amplifier U4 and the second end grounded; the first end of resistor R10 is connected to the negative input terminal of amplifier U4, and the second end is connected to the output terminal Vout3 of amplifier U4; the first end of resistor R11 is connected to the negative input terminal of amplifier U4, and the second end is grounded.

[0042] The second-stage second-order active bandpass multiple feedback circuit adopts an infinite gain multiple feedback active filter structure, including: amplifier U5, resistors R12, R13, and R14, capacitors C24 and C25; the first terminal of resistor R12 is connected to the output terminal Vout3 of the second-stage LC parallel resonant filter amplifier circuit, and the second terminal is connected to the first terminal of resistor R13, the first terminal of capacitor C24, and the first terminal of capacitor C25; the first terminal of resistor R13 is connected to the second terminal of R12, and the second terminal is grounded; the first terminal of capacitor C24 is connected to the second terminal of resistor R12, and the second terminal is connected to the output terminal Vout4 of amplifier U5; the first terminal of capacitor C25 is connected to the second terminal of resistor R12, and the second terminal is connected to the negative input terminal of amplifier U5; the first terminal of resistor R14 is connected to the output terminal Vout4 of amplifier U5, and the second terminal is connected to the negative input terminal of amplifier U5; the positive input terminal of amplifier U5 is grounded.

[0043] The high-frequency weak echo current signal input is used to receive the input current signal and transmit the current signal to the echo signal IV conversion and amplification module.

[0044] The echo signal IV conversion and amplification module is a transimpedance amplifier circuit designed using the LTC6268-10 as the amplifier. The input signal is filtered by a filter capacitor to remove DC noise, and feedback resistors are connected at the inverting input and output terminals. The deep negative feedback formed in the circuit transmits the ultrasonic signal received by the transducer back. The weak current signal returned is converted into a voltage output signal, and a feedback capacitor is connected in parallel across the feedback resistor, which can effectively eliminate the severe self-excited oscillation and tailing phenomenon in the circuit signal. It can more intuitively detect weak high-frequency ultrasonic echo signals from the noise. A resistor and capacitor are connected in parallel to form a low-pass filter, which is connected to the non-inverting terminal of the amplifier to filter out high-frequency noise in the input signal.

[0045] The feedback resistor R of the IV conversion circuit f The resistance value can be calculated using formula (1):

[0046]

[0047] In the formula V outmax Indicates the maximum output voltage, V outmin I represents the minimum output voltage. inmax This indicates the maximum input current.

[0048] The value of the feedback capacitor in the IV conversion circuit can be calculated using formula (2):

[0049]

[0050] In the formula Rf C represents the feedback resistor. f Indicates the feedback capacitor, F bw Indicates bandwidth.

[0051] The echo signal IV conversion module uses the LTC6268-10 as the core unit of the amplifier circuit. The initial signal is a weak current signal of 30nA. After the IV conversion circuit amplifies it once, the resulting proportional weak voltage signal reaches the 20mV level, which meets the requirements of subsequent analog-to-digital conversion. However, after filtering by the Bajie Butterworth bandpass filter module, the amplitude of the signal will be attenuated to a certain extent. Therefore, a 2V / V amplification is required in the subsequent filtering circuit to meet the voltage requirements of subsequent analog-to-digital conversion.

[0052] The eighth-order Butterworth bandpass filter module has a center frequency of 3MHz, a bandwidth of 1.5MHz (passband frequency of 2.25MHz to 3.75MHz), a stopband frequency of 6MHz, a passband attenuation of 3dB, a stopband attenuation of 45dB, and a gain of 2V / V. It can filter out high-frequency and low-frequency noise from the 20mV level voltage signal output by the IV conversion module, attenuate self-excited oscillation, and amplify it by 2 times.

[0053] Furthermore, the eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multi-feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multi-feedback circuit. Both the first-stage and second-stage second-order active bandpass multi-feedback circuits are infinite-gain multi-path multi-feedback active filter structures; the first-stage second-order active bandpass multi-feedback circuit is used as an example for explanation. Similarly, both the first-stage and second-stage LC parallel resonant filter amplifier circuits are LC parallel resonant filter amplifier structures; the second-stage LC parallel resonant filter amplifier circuit is used as an example for explanation.

[0054] The passband frequency of the second-order active bandpass multi-feedback circuit can be calculated by formula (3):

[0055] BW=f2-f1 (3)

[0056] In the formula, BW represents the bandwidth of the bandpass filter, f2 represents the upper limit of the low-pass frequency, and f1 represents the lower limit of the high-pass frequency.

[0057] The quality factor of the second-order active bandpass multi-feedback circuit can be calculated by formula (4):

[0058]

[0059] In the formula, Q represents the quality factor, f0 represents the center frequency, and BW represents the bandwidth of the bandpass filter.

[0060] The passive capacitor in the second-order active bandpass multi-feedback circuit adopts the formula C8=C9=C, and the capacitor value C is selected according to the capacitance-frequency relationship table. Then, based on the selected gain K... P To calculate the resistance value of the resistive element.

[0061] The gain of the second-order active bandpass multiple feedback circuit can be calculated by formula (5):

[0062]

[0063] In the formula K P This represents the gain of a second-order active bandpass multiple feedback circuit.

[0064] The resistance values ​​of resistors R3, R4, and R5 in the second-order active bandpass multi-feedback circuit can be calculated using formulas (6), (7), and (8):

[0065]

[0066] In the formula, Q represents the quality factor, and K... P This represents the gain of the second-order active bandpass multiple feedback circuit, f0 represents the center frequency, and C is the size of the selected capacitor.

[0067] The resonant frequency of the LC parallel resonant filter amplifier circuit can be calculated by formula (9):

[0068]

[0069] In the formula f r L represents the resonant frequency, C represents the inductance in the LC parallel resonant circuit, and C represents the capacitance in the LC parallel resonant circuit.

[0070] The quality factor of the LC parallel resonant filter amplifier circuit can be calculated by formula (10):

[0071]

[0072] In the formula Q r ω represents the quality factor. r The value represents the resonant angular frequency, L represents the inductance in the LC parallel resonant circuit, and R represents the input resistance.

[0073] The bandwidth of the LC parallel resonant filter amplifier circuit can be calculated by formula (11):

[0074]

[0075] In the formula, BW represents the frequency bandwidth, and fr Q represents the resonant frequency. r This represents the quality factor.

[0076] The in-phase scaling factor of the LC parallel resonant filter amplifier circuit can be calculated by formula (12):

[0077]

[0078] In the formula A u R7 represents the in-phase proportional gain, R8 represents the upper bias resistor, and R8 represents the lower bias resistor.

[0079] Example:

[0080] In this embodiment of the disclosure, a post-processing circuit for weak echo signals from a CMUT sensor is provided, combined with... Figure 1 , Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown, the post-processing circuit for the weak echo signal includes a power supply module unit, a high-frequency weak echo signal input unit, an echo signal IV-to-IV conversion and amplification unit, an eighth-order Butterworth bandpass filter processing unit, and an output unit; wherein:

[0081] The power supply module, based on the CMUT sensor, directly supplies positive 5V and negative 5V to the weak echo signal processing module through VCC and VDD respectively. The modular design greatly reduces the size of the weak echo signal processing system.

[0082] The aforementioned high-frequency weak echo signal input unit, via a 1μF capacitor test port, serves as the input terminal of the post-processing circuit for the high-frequency weak echo signal of the CMUT sensor, receiving the current signal I returned from the CMUT ultrasonic transducer. in It is connected to the echo signal IV conversion and amplification unit.

[0083] The output point Vin of the IV conversion amplifier circuit is used for IV conversion and gain amplification to obtain a 20mV level voltage signal. Vin is then connected to an eighth-order Butterworth bandpass filter for filtering and 2V / V amplification to obtain a 30mV level output voltage signal Vout4.

[0084] According to an embodiment of this disclosure, the IV conversion circuit includes: a filter capacitor C1, a matching resistor R1, a matching capacitor C2, a feedback resistor R2, a feedback capacitor C3, a +5V power supply VCC and a -5V power supply VDD, an amplifier LTC6268-10, a first filter capacitor C4, a second filter capacitor C5, a third filter capacitor C6, and a fourth filter capacitor C7.

[0085] The filter capacitor C1 not only provides a test point to confirm that the signal is within the input current range, but also filters out the DC component of the weak high-frequency echo signal, protects the operational amplifier, and is connected to the next stage IV conversion circuit; the feedback resistor R2 is connected to the signal input and output terminals of the signal amplifier, and the feedback capacitor C3 is connected in parallel across the feedback resistor R2; the entire system is powered by ±5V voltage, the first filter capacitor C4 and the second filter capacitor C5 are connected to the +5V input port of VCC; the third filter capacitor C6 and the fourth filter capacitor C7 are connected to the VDD input port.

[0086] The filter capacitors C4, C5, C6, and C7 are used to filter the input power supply. Typically, a large capacitor is used and a small capacitor is connected in parallel to remove ripple. In a specific embodiment, the large capacitor has a value of 10μF and the small capacitor has a value of 100nF.

[0087] The value of the feedback resistor R2 determines the amplification factor of the system. In a specific embodiment, the current of 30nA is amplified to 20mV. Therefore, in a specific application, the resistance value of the feedback resistor is 1MΩ.

[0088] The feedback capacitor can effectively eliminate self-oscillation. The theoretical value of C3 is 0.045pF. In the specific embodiment, considering the parasitic capacitance carried by the PCB board itself, the final value of C3 is 0.1pF, which has a better effect on eliminating self-oscillation.

[0089] The matching resistor R1 and matching capacitor C2 are connected in parallel to the positive port of the amplifier, which can adjust the system gain and bandwidth and improve system stability. In a specific embodiment, R1 is 50KΩ and C2 is 100nF.

[0090] According to an embodiment of this disclosure, the eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multiple feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multiple feedback circuit.

[0091] The first-stage second-order active bandpass multiple feedback circuit includes: passive resistors R3, R4, and R5; passive capacitors C8 and C9; +5V power supply VCC and -5V power supply VDD; amplifier ADA4857-1; first filter capacitor C10; second filter capacitor C11; third filter capacitor C12; and fourth filter capacitor C13.

[0092] According to an embodiment of this disclosure, the pre-output node Vin is connected to the input Vin of the first-stage second-order active bandpass multi-feedback circuit. A second-order active bandpass filter is designed using the infinite gain multi-path negative feedback method. The characteristic of this method is that the poles of the transfer function always fall within the left half of the s-plane, thus eliminating the need to consider its dynamic stability. R3, R4, R5, C8, and C9 are connected according to... Figure 2 The structure shown is connected to the negative port and the output terminal Vout1 of the amplifier. The passive resistor limits the amplifier's gain, thereby controlling the signal amplitude; the passive capacitor controls the frequency response curve, thus achieving the desired bandpass filtering effect.

[0093] In a specific example, the passive resistor R3 is 205Ω, the passive resistor R4 is 64.9Ω, the passive resistor R5 is 909Ω, and the passive capacitors C1 and C2 are 220pF. Together with the amplifier ADA4857-1, they form a second-order bandpass filter based on the infinite gain multiple feedback method.

[0094] The filter capacitors C10, C11, C12, and C13 are used to filter the input power supply. Typically, a large capacitor is used and a small capacitor is connected in parallel to remove ripple. In a specific embodiment, the large capacitor has a value of 10μF and the small capacitor has a value of 100nF.

[0095] The first-stage LC parallel resonant filter amplifier circuit includes: resonant resistor R6, resonant inductor L1, resonant capacitor C14, voltage divider amplifier resistor R7, voltage divider amplifier resistor R8, +5V power supply VCC and -5V power supply VDD and amplifier ADA4857-1, first filter capacitor C15, second filter capacitor C16, third filter capacitor C17 and fourth filter capacitor C18.

[0096] According to an embodiment of this disclosure, the pre-output node Vout1 is connected to the front end Vout1 of the first-stage LC parallel resonant filter amplifier circuit. An LC parallel resonant filter is formed using resistor R6, inductor L1, and capacitor C14, as shown in the following structure. Figure 3 As shown. When the input signal frequency is lower than the lowest frequency of the passband, the capacitive reactance of the capacitor is very large, making it difficult for the input signal to pass through, and the circuit exhibits inductive impedance. When the input signal frequency is higher than the highest frequency of the passband, the circuit exhibits capacitive impedance. When the input signal frequency is near the resonant frequency, the circuit exhibits resistive impedance, with minimal phase shift. Finally, the filtered signal is amplified by an inverting proportional amplifier composed of amplifier ADA4857-1, voltage divider resistors R7 and R8, and the filtered voltage signal is output at the output terminal Vout2.

[0097] In a specific embodiment, the resonant resistor R6 is 536Ω, the parallel resonant inductor L1 is 6.8μH, the parallel resonant capacitor C14 is 680pF, the voltage divider amplification resistor R7 is 127Ω, and the voltage divider amplification resistor R8 is 75Ω.

[0098] The filter capacitors C15, C16, C17, and C18 are used to filter the input power supply. Typically, a large capacitor is used and a small capacitor is connected in parallel to remove ripple. In a specific embodiment, the large capacitor has a value of 10μF and the small capacitor has a value of 100nF.

[0099] The second-stage LC parallel resonant filter amplifier circuit includes: resonant resistor R9, resonant inductor L2, resonant capacitor C19, voltage divider amplifier resistor R10, voltage divider amplifier resistor R11, +5V power supply VCC and -5V power supply VDD, amplifier ADA4857-1, first filter capacitor C20, second filter capacitor C21, third filter capacitor C22, and fourth filter capacitor C23.

[0100] According to an embodiment of this disclosure, the pre-output node Vout2 is connected to the front end Vout2 of the second-stage LC parallel resonant filter amplifier circuit. An LC parallel resonant filter is formed using resistor R9, inductor L2, and capacitor C19, as shown in the following structure. Figure 4 As shown. When the input signal frequency is lower than the lowest frequency of the passband, the capacitive reactance of the capacitor is very large, making it difficult for the input signal to pass through, and the circuit exhibits inductive impedance. When the input signal frequency is higher than the highest frequency of the passband, the circuit exhibits capacitive impedance. When the input signal frequency is near the resonant frequency, the circuit exhibits resistive impedance, with minimal phase shift. Finally, the filtered signal is amplified by an inverting proportional amplifier composed of amplifier ADA4857-1, voltage divider resistors R10 and R11, and the filtered voltage signal is output at the output terminal Vout3.

[0101] In a specific embodiment, the resonant resistor R9 is 536Ω, the parallel resonant inductor L2 is 3.9μH, the parallel resonant capacitor C19 is 430pF, the voltage divider amplification resistor R10 is 100Ω, and the voltage divider amplification resistor R11 is 59Ω.

[0102] The filter capacitors C20, C21, C22, and C23 are used to filter the input power supply. Typically, a large capacitor is used and a small capacitor is connected in parallel to remove ripple. In a specific embodiment, the large capacitor has a value of 10μF and the small capacitor has a value of 100nF.

[0103] The second-stage second-order active bandpass multiple feedback circuit includes: passive resistors R12, R13, and R14; passive capacitors C24 and C25; +5V power supply VCC and -5V power supply VDD; amplifier ADA4857-1; first filter capacitor C26; second filter capacitor C27; third filter capacitor C28; and fourth filter capacitor C29.

[0104] According to an embodiment of this disclosure, the pre-output node Vout3 is connected to the input terminal Vout3 of the second-stage second-order active bandpass multi-feedback circuit. The second-order active bandpass filter is designed using the infinite gain multiple negative feedback method. A characteristic of this method is that the poles of the transfer function always fall within the left half of the s-plane, thus eliminating the need to consider its dynamic stability. R12, R13, R14, C24, and C25 are connected according to... Figure 5 The structure shown is connected to the negative port and the output terminal Vout4 of the amplifier. The passive resistor limits the amplifier's gain, thereby controlling the signal amplitude; the passive capacitor controls the frequency response curve, thus achieving the desired bandpass filtering effect.

[0105] In a specific example, the passive resistor R12 is 422Ω, the passive resistor R13 is 56.26Ω, the passive resistor R14 is 909Ω, and the passive capacitors C24 and C25 are 270pF. Together with the amplifier, they form a second-order bandpass filter based on the infinite gain multiple feedback method.

[0106] The filter capacitors C26, C27, C28, and C29 are used to filter the input power supply. Typically, a large capacitor is used and a small capacitor is connected in parallel to remove ripple. In a specific embodiment, the large capacitor has a value of 10μF and the small capacitor has a value of 100nF.

[0107] In a specific example, the circuit was simulated and tested using LTspice XVII software. The LTC6268-10 model and ADA4857-1 model were downloaded from the ADI website and imported into LTspice XVII software. The IV conversion amplifier circuit and the eighth-order Butterworth bandpass filter circuit were built according to the description. The parameters of each component were preset to be consistent with the previous description, and frequency scanning was performed.

[0108] In a specific example, the gain-Baud simulation diagram of the IV-to-Voltage converter amplifier circuit is as follows: Figure 7As shown in the simulation results, the IV converter amplifier circuit can reach a frequency of 3.56MHz at -3dB, which meets the amplification requirements of the system operating at 3MHz. At this point, the amplification gain of the IV converter amplifier circuit is 117.004dB, and calculations show that it can amplify a 30nA current signal to 21.2mV. After filtering by an eighth-order Butterworth bandpass filter, the gain Bode plot of the IV converter amplifier circuit + eighth-order Butterworth bandpass filter circuit is shown in the simulation diagram. Figure 8 As shown, simulation results indicate that the actual bandwidth of the system is 1.6MHz, the center frequency is 3.09MHz, the filtering range of the eighth-order Butterworth bandpass filter is 2.29MHz to 3.9MHz, and the gain at -3dB is 11.8953dB. At this point, the input voltage signal can be amplified to 26.6mV, meeting the amplification and filtering requirements of the system operating at 3MHz. In summary, this disclosure provides a post-processing circuit for weak echo signals from CMUT sensors, including a DC filter circuit, an IV conversion circuit, and an eighth-order Butterworth bandpass filter circuit, achieving higher gain and bandwidth performance than traditional two-stage amplifier circuits and bandpass filter structures.

Claims

1. A post-processing circuit for weak echo signals from a CMUT sensor, characterized in that, It includes a forward voltage input module, a reverse voltage input module, an echo signal IV conversion and amplification module, and an eighth-order Butterworth bandpass filter module; The forward voltage input module is connected in sequence to the forward power input port of the echo signal IV-to-conversion amplifier module and the forward power input port of the eighth-order Butterworth bandpass filter module; the reverse voltage input module is connected in sequence to the reverse power input port of the echo signal IV-to-conversion amplifier module and the reverse power input port of the eighth-order Butterworth bandpass filter module; the output port of the echo signal IV-to-conversion amplifier module is connected to the input port of the eighth-order Butterworth bandpass filter module.

2. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 1, characterized in that, The eighth-order Butterworth bandpass filter module consists of a first-stage second-order active bandpass multi-feedback circuit, a first-stage LC parallel resonant filter amplifier circuit, a second-stage LC parallel resonant filter amplifier circuit, and a second-stage second-order active bandpass multi-feedback circuit. The output port of the echo signal IV conversion amplifier circuit is connected to the input port of the first-stage second-order active bandpass multi-feedback circuit; the output port of the first-stage second-order active bandpass multi-feedback circuit is connected to the input port of the first-stage LC parallel resonant filter amplifier circuit; and the output port of the first-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage LC parallel resonant filter amplifier circuit. The output port of the second-stage LC parallel resonant filter amplifier circuit is connected to the input port of the second-stage second-order active bandpass multiple feedback circuit.

3. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 2, characterized in that, In the positive voltage input module, the VCC input port is connected to the positive voltage input port 6 of the IV conversion amplifier chip U1, the positive voltage input port 7 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the positive voltage input port 7 of the first-stage LC parallel resonant filter amplifier circuit U3, the positive voltage input port 7 of the second-stage LC parallel resonant filter amplifier circuit U4, and the positive voltage input port 7 of the second-stage second-order active bandpass multi-feedback amplifier chip U5; capacitors C4 and C5 are connected in parallel, with the first end connected to the positive voltage input port 6 of the IV conversion amplifier chip U1 and the second end grounded; capacitor C10 and capacitor C5 are connected in parallel. Capacitor C11 is connected in parallel, with its first end connected to the positive voltage input port 7 of the amplifier chip U2 in the first-stage second-order active bandpass multiple feedback circuit, and its second end grounded; capacitors C15 and C16 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U3 in the first-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C20 and C21 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U4 in the second-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C26 and C27 are connected in parallel, with their first end connected to the positive voltage input port 7 of the amplifier chip U5 in the second-stage second-order active bandpass multiple feedback circuit, and their second end grounded.

4. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 3, characterized in that, In the reverse voltage input module, the VDD input port is connected to the reverse voltage input port 2 of the IV conversion amplifier chip U1, the reverse voltage input port 4 of the first-stage second-order active bandpass multi-feedback amplifier chip U2, the reverse voltage input port 4 of the first-stage LC parallel resonant filter amplifier circuit U3, the reverse voltage input port 4 of the second-stage LC parallel resonant filter amplifier circuit U4, and the reverse voltage input port 4 of the second-stage second-order active bandpass multi-feedback amplifier chip U5, respectively; capacitors C6 and C7 are connected in parallel, with the first end connected to the reverse voltage input port 2 of the IV conversion amplifier chip U1 and the second end grounded; capacitor C12 and capacitor C7 are connected in parallel. Capacitor C13 is connected in parallel, with its first end connected to the inverted voltage input port 4 of the amplifier chip U2 in the first-stage second-order active bandpass multiple feedback circuit, and its second end grounded; capacitors C17 and C18 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U3 in the first-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C22 and C23 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U4 in the second-stage LC parallel resonant filter amplifier circuit, and their second end grounded; capacitors C28 and C29 are connected in parallel, with their first end connected to the inverted voltage input port 4 of the amplifier chip U5 in the second-stage second-order active bandpass multiple feedback circuit, and their second end grounded.

5. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 4, characterized in that, In the echo signal IV conversion and amplification module, resistor R1 and capacitor C2 are connected in parallel, with the first end connected to the positive input terminal of amplifier U1 and the second end grounded; resistor R2 and capacitor C3 are connected in parallel, with the first end connected to the inverting input terminal of amplifier U1 and the second end connected to the output terminal Vin of amplifier U1; the first end of capacitor C1 is connected to the echo signal input terminal Iin, and the second end is connected to the inverting input terminal of amplifier U1.

6. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 5, characterized in that, In the first-stage second-order active bandpass multiple feedback circuit, the first end of resistor R3 is connected to the output terminal Vin of the echo signal IV conversion amplification module, and the second end is connected to the first end of resistor R4, the first end of capacitor C8, and the first end of capacitor C9; the second end of resistor R4 is grounded; the second end of capacitor C8 is connected to the output terminal Vout1 of amplifier U2; the second end of capacitor C9 is connected to the inverting input terminal of amplifier U2; the first end of resistor R5 is connected to the output terminal Vout1 of amplifier U2, and the second end is connected to the inverting input terminal of amplifier U2; the non-inverting input terminal of amplifier U2 is grounded.

7. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 6, characterized in that, In the first-stage LC parallel resonant filter amplifier circuit, the first end of resistor R6 is connected to the output terminal Vout1 of the first-stage second-order active bandpass multiple feedback circuit, and the second end is connected to the positive input terminal of amplifier U3; inductor L1 and capacitor C14 are connected in parallel, with the first end connected to the positive input terminal of amplifier U3 and the second end grounded; the first end of resistor R7 is connected to the inverting input terminal of amplifier U3, and the second end is connected to the output terminal Vout2 of amplifier U3; the first end of resistor R8 is connected to the inverting input terminal of amplifier U3, and the second end is grounded.

8. The post-processing circuit for weak echo signals of a CMUT sensor according to claim 7, characterized in that, In the second-stage LC parallel resonant filter amplifier circuit, the first end of resistor R9 is connected to the output terminal Vout2 of the first-stage LC parallel resonant filter amplifier circuit, and the second end is connected to the positive input terminal of amplifier U4; inductor L2 and capacitor C19 are connected in parallel, with the first end connected to the positive input terminal of amplifier U4 and the second end grounded; the first end of resistor R10 is connected to the inverting input terminal of amplifier U4, and the second end is connected to the output terminal Vout3 of amplifier U4; the first end of resistor R11 is connected to the inverting input terminal of amplifier U4, and the second end is grounded.

9. A post-processing circuit for weak echo signals of a CMUT sensor according to claim 8, characterized in that, In the second-stage second-order active bandpass multiple feedback circuit structure, the first terminal of resistor R12 is connected to the output terminal Vout3 of the second-stage LC parallel resonant filter amplifier circuit, and the second terminal is connected to the first terminal of resistor R13, the first terminal of capacitor C24, and the first terminal of capacitor C25; the second terminal of resistor R13 is grounded; the second terminal of capacitor C24 is connected to the output terminal Vout4 of amplifier U5; the second terminal of capacitor C25 is connected to the inverting input terminal of amplifier U5; the first terminal of resistor R14 is connected to the output terminal Vout4 of amplifier U5, and the second terminal is connected to the inverting input terminal of amplifier U5; the non-inverting input terminal of amplifier U5 is grounded.

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